1. Field of the Invention
The present invention relates to the automated movement of a laser peening head and particularly to the automated positioning of that mobile laser peening head.
2. Description of the Related Art
Current laser peening is typically performed within fixed processing cells. The laser is stationary and the beam delivery system, which transfers the laser beams to a processing cell, is also typically stationary. This results in a fixed laser beam position within the processing cell. A workpiece undergoing laser peening must be moved through the path of the fixed laser beams in a pre-programmed positioning sequence to complete laser peening of the part over the prescribed area on the workpiece.
This program of sequential positions of the workpiece may include a large number of positioning movements to cover the desired laser peened area with a multiplicity of laser peened spots. Each spot represents one position of the workpiece and one laser pulse applied to the workpiece surface. This method has served well for workpieces of relatively small size that can be conveniently moved to a stationary processing cell and manipulated within the cell by a reasonably sized machine tool such as a robot.
However, when extending the use of laser peening to very large structures, such as aircraft wing and fuselage components, it is no longer feasible to construct processing cells and machine tools large enough to process the desired areas on these structures. To laser peen these types of large structures, it is most feasible to use a mobile laser and/or mobile laser beam delivery system to bring the laser beam to the area on the structure to be laser peened, and to reduce the processing cell to a small, mobile processing head that can be easily manipulated over the surface of the area to be laser peened on the surface (see U.S. patent application Ser. Nos. 09/211,553 and 09/846,084, both commonly assigned herewith and fully incorporated by the reference thereto).
The processing head must be able to move over the surface of the area on the structure being processed and to deliver the laser beam and any required overlay materials to the area being processed reproducibly and accurately to accomplish consistent, useful laser peening of the structure. An extremely important step in the processing sequence is to accurately position the laser beam on the surface of the structure. In a stationary workcell wherein smaller workpieces are manipulated in a fixed laser beam path, methods to ensure the proper positioning of the workpiece within the laser beam to accurately laser peen the intended target area are described in an earlier patent application structures (i.e., U.S. patent application Ser. No. 09/564,360, commonly assigned herewith and fully incorporated by reference thereto). That application also addresses manual or operator-controlled positioning of the mobile laser peening head and firing of the laser for each laser pulse for large, stationary. For exfoliation corrosion detection on large structures using a laser peening-related method, a patent filing includes the indexed movement of a robotic laser peening head over a large structure (i.e., U.S. patent application Ser. No. 09/846,08′).
U.S. patent application Ser. No. 09/21,553, concerning a mobile laser peening system, describes a remote processing head, but utilizes operator guidance and alignment of the processing head for each laser pulse through a direct visual system or remote camera viewing system. Automated movement of the head according to a preprogrammed spatial pattern and automated application and/or removal of the overlays is not mentioned.
U.S. patent Application No. 09/846,084, from which this application depends, describes an automated laser search peening head for exfoliation corrosion detection. It specifies automated movement of a robotic processing head over a surface to specific locations and describes indexing the movement of the robot over the surface. However, it does not describe automated location verification methods to be used. The application does not describe automated application and removal of overlays but does describe sequential control of overlay application, laser pulse application, and surface examination for corrosion by a controller.
U.S. Pat. No. 5,790,620, to Okazaki et al, describes a processing head for laser peening underwater in a nuclear reactor shroud and core cooling piping. There is pre-mapping of the interior surfaces by the camera, and subsequent programming of a processing location and pattern into a controller for the processing head. The movement of the processing head or mirror system and lens focusing system within the processing head are automated, being controlled by a controller. Since the operation is carried out under water, there is no automated application of opaque or transparent overlays. The surfaces are processed without an opaque overlay. The programmed motion of the head does not address automated real time location verification and correction to a programmed position on a large structure.
What is needed is an automated method and apparatus to control the movement and positioning of the mobile processing head over the surface of the structure to be laser peened, and in addition to instruct the laser to pulse when the processing head is in upper position and she surface has been made ready for the laser pulse.